opthalmic drug delivery Flashcards
Why is it difficult to deliver drugs to the eye?
Challenges include blinking reflex, tear flow, a hard outer layer, lack of direct blood supply to the cornea, and the blood-retinal barrier at the back of the eye.
What is the typical bioavailability of eye drops in the aqueous humor?
Only about 5% of the drug reaches the aqueous humor due to rapid drainage and tear turnover.
How can bioavailability in ophthalmic drug delivery be improved?
- By reducing drainage (using viscosity enhancers, gels, ointments, and emulsions)
- enhancing corneal penetration with prodrugs, penetration enhancers, and nanoparticles.
What is the role of viscosity enhancers in ophthalmic drugs?
They increase contact time of the drug with eye tissues, reducing drainage. Optimal viscosity is 12-25 mPa.s for ocular delivery.
Why are ointments recommended for nighttime use in ocular delivery?
They reduce drainage and improve drug retention but can blur vision, making them suitable for use before sleep.
What do penetration enhancers do in ophthalmic drug delivery?
They disrupt cellular tight junctions to allow easier drug entry but may damage cells; amphiphilic polymers are safer alternatives.
How do prodrugs improve drug penetration in the eye?
Prodrugs like diesterified adrenaline are more lipophilic, enhancing corneal absorption. They are converted back to active form by corneal enzymes.
What is the benefit of using nanoparticles for ocular drug delivery?
Nanoparticles are slowly eliminated, can be bioadhesive, and penetrate through paracellular and transcellular routes, prolonging drug action.
What are Ocusert® and Lacrisert® used for in ophthalmic drug delivery?
Ocusert® provides a constant release of pilocarpine for glaucoma, and Lacrisert® is a hydroxypropyl cellulose insert for dry eye treatment.
What are iVation and Port systems used for?
iVation (a titanium coil with triamcinolone) treats diabetic macular edema; the Port system releases ranibizumab for age-related macular degeneration and other eye conditions.
How does gene therapy work in treating eye diseases?
Gene therapy replaces faulty genes to treat disease, often using inactive viruses as delivery vehicles to target cells in the eye.
